I use KMail because Thunderbird is extremely slow with external ssh access (KDE3.5/4.1 Mandriva 2009). I discovered an unusual behavior which was not present in the earlier versions.

When saving attachments it is often necessary to rename them. For instance you get attachments "IMG00025976.JPG", "IMG00025977.JPG" and "IMG00025978.JPG" probably you want to save them as "Board_front_a.jpg", "Board_front_b.jpg", "Board_front_c.jpg". Earlier the standard procedure to do this was to give the new name for the first file, and when saving the second and third ones clicking on the first file's name and change "_a" to "_b" and "_c". Now, with the new KMail this is not possible. When storing the second file you click the first name, KMail asks if you want to overwrite the first one. If you respond "no", you can start the save procedure again. Thus you have to type the new names many times again and again.

This is a minor issue, but when saving many attachments you surely wish the old KMail procedure back.